Many types of heat exchangers in use today employ two headers spaced apart and interconnected by a plurality of parallel, open ended tubes. A plurality of openings in the headers receive the open ends of the heat exchange tubes yet to place the headers in fluid communication. Air or some other fluid then passes over the tubes and exchanges heat energy with the fluid flowing through the tubes. Often, a plurality of plate or serpentine fins are disposed over the entire tube length between the headers to increase the surface area available for exchanging heat.
Typical applications for heat exchangers are car or truck radiators and condensers. Heat exchangers may also be found in commercial processes or as one component in a much larger system.
In manufacturing tubular heat exchangers, a plurality of holes must be formed in each of the headers to receive the heat exchange tubes. Because forming these holes structurally weaken the header, it is useful to retain the metal moved from the hole area and form a flange around the hole as described in U.S. Pat. No. 3,689,972. Unfortunately, forming the hole can produce warping of the header or uneven hole edges. Either of these defects reduces the accuracy of the hole curvature which reduces the seal around the hole.
Another option is to construct the heat exchange header with a dome between the heat exchange tube connector holes. Such a construction is shown in U.S. Pat. No. 4,615,385. The use of a dome, however, can lead to uneven flow of the heat exchange fluid around the heat exchange tubes and between the fins. The domed surface between the header surface and the first row of fins exhibits a greater cross sectional area than other passages through the fins. This excess area provides a path of lower resistance to fluid flow. As a result, heat exchange fluid tends to flow through these larger spaces rather than through the passages between fins. This flow pattern reduces the effectiveness of the heat exchanger.
Additionally, the shape of the passage between the header, the fin, and the heat exchange tube exhibits a configuration that promotes the retention of water or other liquids. The curving surface of the header meets the tube in a narrowing passage that ends in a point. Water is held in that narrowing passage by capillary action thereby accelerating exterior corrosion of both the header and the heat exchange tubes. This relationship is illustrated in the attached FIG. 1.
In FIG. 1, annular depression 7 is bounded by the exterior of heat exchange tube 2, the lower surface of serpentine fins 4, and the exterior surface of header dome 11. Each side of dome 11 will form an annular depression 7.
When used for heat exchange with air, flowing air tends to pass through depression 7 rather than gaps 41 because the flow resistance through gaps 41 is greater than that of depression 7. Therefore, more air flows through depression 7 and at a higher velocity than the air passing through gaps 41. This is not the flow pattern for which heat exchangers are optimized, and the efficiency of heat-exchanging is less than it could be.
When the heat exchanger is used for heating a relatively cooler air, condensed water 42 from the warmer air accumulates in depression 7 due to capillary action between tube 2 and dome 11. If water accumulates in depression 7 for long enough, corrosion begins to weaken both header 1 and tube 2. Accordingly, the air must be dried before contact with the heat exchanger to minimize condensation. This extra equipment reduces the cost efficiencies associated with the heat exchange processes.
It would be desirable to have a way to form heat exchange tube connector holes without introducing dimensional inaccuracies in the hoe shape or warping the header.
It would also be desirable to have a way of reducing or eliminating the excess cross sectional area differences between the header and the cooling fins without adversely affecting the structural integrity of the header or the seal between the header and the heat exchange tubes.
It would further be desirable to reduce the excess area without harming the hermetic seal between the header and the heat exchange tubes.